Experience has shown that the catastrophic failure of an integrated circuit chip, such as a microprocessor, will typically occur during the initial phase of the chip life. If the chip passes its initial operational phase, the life and reliability of the chip will have a relatively high probability.
In the case of a burn-in test socket, to precipitate early chip failure, the chip is "exercised" or powered while being subjected to relatively high external temperatures. Typically, a batch of chips is electrically powered in an oven where the temperature is maintained at approximately 150.degree. C. for an extended period of time, such as 1,000 hours. This is referred to in the art as "burn-in".
During burn-in, a batch of chips may be mounted on a mother board, and the chip leads are electrically connected to respective circuit elements on the other board by a suitable means, such as one or more flexible electrical connectors. Maintaining good electrical contact between the chip leads and the flexible electrical connector is very important. Where the leads are gold plated, the electrical contact is usually not a major problem; but where the chip leads are tin plated, a relatively high retention force is necessary to assure good electrical contact. This is due to oxidation of the tin-plated chip leads. Even if the oven has a nitrogen atmosphere, it is still necessary to maintain a relatively-high clamping force to retain the chip frames and assure good electrical contact with the chip leads.
In order to assure a proper and sufficient retention force, especially where the chip leads are tin-plated, a system of levers or oversized latches are usually necessary in order to achieve the necessary mechanical advantage for the desired retention force. However, because of space problems, this is not feasible nor particularly desirable since it reduces the total number of chips on the board and thus reduces production rates.
For large batches of chips, the testing apparatus is fully automated and includes robotics arms for transferring the batches of chips into and out of the oven. In production, and because of the relatively large number of chips being burn-in, the prior clamping mechanisms interfered with the high-speed automated apparatus for transferring large batches of chips.
In accordance with prior art practices and practitioners, it was known that in order to achieve proper electrical contact, a force had to be applied between the two connecting surfaces. Further, it was important to maintain an optimal force range during the high temperature testing of the assembly. Normally, the socket is designed so that when the lid of the test socket is closed a constant force is applied. However, due to the often extensive mechanical tolerance build-up that can exist among the apparatus components, such as the latch, lid, pusher, device elements, and socket base, it was extremely difficult to determine the actual size of the applied force. This led to inaccurate or incomplete testing.
The copending application represents a major effort to overcome the shortcomings of the prior art. The invention thereof is directed to a burn-in socket testing apparatus and comprises a first frame member for mounting to a planar electronic board, such as a mother board, where such first frame member includes electrical means for engaging the chip leads or traces of the chip to be tested, and applying electrical current during burn-in. Above the first frame member is a second frame member disposed in sliding engagement therewith, where the second frame member is movable from a first position to a second position. Finally, cooperative latching and camming means are provided between the first and second frame members to effect the movement between the first and second positions, and to securely hold the chip during burn-in, where the camming means includes a pivotal member movable from a remote position free of the chip to a position engaging the chip.
The present invention teaches a spring loaded, floating cover member which eliminates most of the mechanical tolerance build-up which can be detrimental to the performance of this type of socket, particularly in the operation of a burn-in test socket. The unique features hereof will become apparent in the description which follows, particularly when read in conjunction with the accompanying drawings.